july 11 -- july 23, 1999 snowmass village, colorado in magnetic confinement … · 1999. 8. 2. ·...

EXCITING OPPORTUNITIESTO ADVANCE FUSION ENERGY

IN MAGNETIC CONFINEMENT CONCEPTS

PRESENTED BY

TONY S. TAYLOR

FOR THE

MAGNETIC FUSION CONCEPT WORKING GROUP

AT THE

1999 FUSION SUMMER STUDYSNOWMASS VILLAGE, COLORADO

JULY 11 -- JULY 23, 1999

MFEWG Snowmass 99 by Taylor 2

Special Thanks To:

MFCWG Convenors

— Herb Berk

— Ray Fonck

— Jim Drake

— Martin Greenwald

— Dave Hill

— Brad Rice

— John Sarff

— Bob Taylor

— Mike Zarnstorff

BREAKOUT GROUP LEADERS

Transport in magnetic confinement concepts

– Martin Greenwald, John Sarff

MHD stability in magnetic confinement concepts

– Ted Strait, Chris Hegna

Plasma boundary and particle control

– Bruce Lipschultz, Tom Rognlien

Achieving steady-state operation in MFE devices

– Hutch Neilson, Ed Synakowski

Burning plasmas in magnetic confinement concepts

— Raffi Nazikian, Wayne Houlberg

MFE concept integration & performance measures

— Mike Zarnstorff, Stan Luckhardt

Complementarity of MFE Research PortfolioTargets Critical Issues

¥ Classify by degree of externalmagnetic control vs ability ofplasma to organize itself

¥ Strong degree ofcomplementarity andcommonality in concepts

Ð Study of one enhances ability todevelop others

WeakExternal

Field

StrongExternal

Field

Concepts

Spheromak

Reversed-Field Pinch

SphericalTorus

Tokamak

Stellarator

Self-Organized

ExternalControl

FRC

(q > 1)

(q < 1)


Elements of a Scientific Roadmap for MFE

Steady-State

Integration

Burning Plasma

MHD Transport Boundary

PlasmaScience &

Technology

Tokamak

ST

Stellarator RFP

FRC

Spheromak

Other Magnetic

TECHNOLOGIES

EC: D. Barnes


The Goals of MFE Research

Determine the optimum magnetic configuration(s) for attractive fusionenergy production, by ...

• Using a spectrum of magnetic configurations ranging from externally-controlledto self organized, to ...– Understand the scientific foundations of MFE (equilibrium and

stability, transport, boundary, plasma control), and to..– Integrate these elements to optimize a steady-state, high-performance

magnetic fusion plasmaBe prepared to move forward with the next stage of MFE

development— Burning Plasma (JET-Upgrade, FIRE, Ignitor)– Steady State (KSTAR, …)– Integrated test of sustained burning plasma (ITER-RC)

Participate in the ITER-RC if EU or Japan decide to construct


MFE Goals (cont.)

¥ Provide fertile environment for new ideas and innovationin MFEÐ New confinement concepts, improvements/hybrids of

existing conceptsÐ Cross-fertilization of ideas and research across concepts

Two over-arching themes have emerged from theMFCWG discussions

Across Magnetic Concepts and Across Scientific Disciplines

• Physics Understanding and Predictive Capability to Develop theScientific Basis for Fusion Energy– Allows (fosters) commonality across concepts and levels of development— Transferability of physics learned from one magnetic concept to another— Rapid development of concepts (possibly skipping a level)— Opportunity to reduce the cost of fusion energy development

Optimal design of experiments/facilities— rapid development• Development and employment of plasma control tools

— Scientific Understanding— Performance optimization— Innovative technological and scientific solutions

⇒ Partnership between technology & physics

Elements required for physics understanding and predictive capability

¥ Innovative, comprehensive diagnostic measurements areessential

¥ Operational time for detailed scientific investigation

¥ Strong coupling between theory, modeling, andexperiment

¥ Inclusion of more complete plasma physics and detailedgeometric effects into modeling codes using advancedcomputational tools

¥ Control tools for detailed physics investigation

¥ Program emphasis: strong focus on science


MHD Stability in the MFE Roadmap

Steady-State

Integration

Burning Plasma


PlasmaScience &

Technology

Tokamak

ST

Stellarator RFP

FRC

Spheromak


Improving plasma stability: Issues & Opportunities

¥ Critical issue: Fusion performance improves with beta, but É..MHD instabilities often limit performance at high beta.Ð Ideal Kink/Ballooning Modes (limits are well understood)Ð Tearing Modes (including Neoclassical)Ð Resistive Wall ModesA possible consequence of violating stability boundaries is a disruption

¥ Opportunity: Configuration innovation extends stability boundariesÐ 2D and 3D discharge shaping, helical coils

(2-D): C-MOD, DIII-D, NSTX, MAST, É (3D): NCSXÐ Profile modifications at low aspect ratio MAST, NSTX, PegasusÐ Suppression of instabilities by negative magnetic shear LHD, NCSX,

Reversed-Shear TokamaksÐ Flowing liquid lithium wall New concept, needs further evaluation


Improving plasma stability - Opportunities

¥ Avoidance of instabilities:Ð Optimization of pressure and current profiles Many DevicesÐ Active feedback control of profiles (ASDEX-U, C-MOD, DIII-D, JET, JT-60U, MST)Ð Rotational stabilization Very high natural rotation (ST, Spheromak, FRC),or driven rotation (ET)

¥ Active control of MHD modesÐ Feedback stabilization by localized RF current drive

ASDEX-U, COMPASS-D (now); DIII-D (2000)Ð Feedback stabilization by external coils DIII-D, HBT-EP (1999-2003); need concept exploration for RFP.

ýDisruption Mitigationý neutral point operation (JT-60U), solid or gas injection (C-MOD, JT-60U, ASDEX,

DIII-D); liquid jet


Beyond Standard MHD

¥ Critical issue: Ideal and resistive MHD has had much quantitative success, but ...Standard ideal and resistive MHD is not sufficient to describe some magneticconfigurations and observed phenomena.

¥ Opportunity: Develop and apply analytic theory and predictive codes with:Ð Flow, flow shear (equilibrium, relaxation, stability: RWM, ...)Ð Neoclassical effects (resistive stability: NTM, ...)Ð 2-fluid physics (equilibrium and stability)Ð Finite Larmor radius (ideal and resistive stability)Ð Kinetic effects (energetic particle instabilities: TAE, ...)Ð 3D magnetic field structure (islands, stochasticity)

ý Linear and nonlinear, 2-D and 3-D analytic theory and fluid-based codes are anopportunity to include these additional physics effects for all configurations.

ý Need to support both analytic theory and large scale code development, andencourage coupling of theory/ numerics/experiment.


Transport in the MFE Roadmap

Steady-State

Integration

Burning Plasma


PlasmaScience &

Technology

Tokamak

ST

Stellarator RFP

FRC

Spheromak

Taylor Snowmass p1

Transport Issues

1. Need for science based predictive capability for transportincluding density limits.Ð Empiricism useful but can only take us so farÐ Special requirements

¥ Particle and impurity transport¥ Electron thermal transport¥ Neo-classical transport¥ Dynamics

Why is solving this essential?

¥ Confidence in designÐ Reduce uncertainty and costs for Ònext stageÓ for all

concepts at any stage of development.Ð Ability to transfer physics experience between concepts

¥ Enable rapid innovation of new or improved concepts

¥ Turbulent transport as physics Ògrand challengeÓ

Taylor Snowmass p2

Transport Opportunities

Develop physics based predictive capability

¥ Improve experimental/theory/computation cooperation andcomparison

¥ Key additional physics in turbulence simulationsÐ Electromagnetics, electron, and impurity dynamicsÐ General geometryÐ FlowsÐ edge/core coupling

¥ Extend diagnostic coverage of turbulence (core and edge)Ð Measure key quantities over a wide range

of spatial scalesÐ Employ new ways of measuring and analyzing

turbulence (imaging, cross phase measurements,synthetic diagnostics from simulations, É)

Ð Pursue innovation¥ Marshal additional resources

Ð Machine run time and port spaceÐ Turbulence and transport studies in new facilities (from

basic plasma to burning plasma experiments)Ð Exploit next generation computing capabilitiesÐ Pursue interconcept studies

n, ϕ, T, B∼ ∼ ∼ ∼

Taylor Snowmass p3

Need to Control Turbulence & Transport

This implies control of density, temperature, current andflow profiles

Why essential?

¥ Improve performance (eg. β, τ, , etc.)

¥ Control pressure and current profiles consistent withMHD stability

¥ Optimize profiles for bootstrap current Ð steady state(relax current drive requirements)

¥ Formation and dynamic control of bifurcations andtransport barriers

Opportunities

¥ Deploy and test toolsÐ Flow control, particularly RF driveÐ Current driveÐ Density control/fuelingÐ Power deposition

¥ Profile diagnostics (eg Vθ)

¥ Demonstrate integrated high β, enhancedconfinement, steady state operation

¥ Integrate theoretical modeling in control design


Boundary Plasma in the MFE Roadmap

Steady-State

Integration

Burning Plasma


PlasmaScience &

Technology

Tokamak

ST

Stellarator RFP

FRC

Spheromak

Plasma Boundary: We have a solution for aconventional Tokamak

¥ We have a reasonable scientific basis for a conventionallong-pulse tokamak divertor solution at high density(collisional edge, detached)Ð Low Te recombining plasma leads to low heat and particle fluxes at

wallÐ Adequate ash control, compatible with ELMing H-mode confinementÐ Appropriate for future tokamaks (e.g. to high density ITER-RC)Ð We have concerns about simultaneously handling disruptions/ELMs

and tritium inventory which shorten divertor lifetime

¥ The challenge is to find self-consistent operating modesfor other configurations ...

There are common boundary control ISSUES & OPPORTUNITIESthat must be addressed to move MFE concepts forward

1. Extend boundary control techniques to lower-collisionalityplasmas and other magnetic geometries

¥ Poloidal Divertor at low density for current drive (AT, ST, Spheromak)

¥ Non-axisymmetric magnetic geometries (Stellarator, RFP)

¥ Radiative Mantle (all)

¥ Kinetic effects, drifts (all); large mirror ratio (ST and LDX)

2. Develop control of impurity sources & transport to maximizeboundary radiation and core cleanliness

¥ Flow control techniques, e.g. induced SOL ion flow, neutral flow valve(Tokamaks, ST)

¥ Better impurity source and transport characterization (all)

¥ Biasing, helicity injection, RF launchers (Tokamaks, ST, Spheromak,Mirrors)

Boundary ISSUES & OPPORTUNITIES (cont)

3. Develop reactor-relevant materials (e.g. low T retention andradiation effects) compatible with clean core plasmas

¥ Solid Low-Z, e.g. Be (JET, move away from graphite)

¥ Solid High-Z (Mo in C-Mod)

¥ Liquid Surfaces, e.g. Li, FLIBE, etc.(no MFE devices yet, Li Divertor CDX-U)

¥ Disruption mitigation, e.g. He puff, solid pellets (several)

4. Develop physics understanding of core-edge coupling¥ Diagnosis and modeling of transport in presence of open field lines,

particularly J, no, and flow in edge (RFP, Tokamaks, Stellarator, ST)

¥ Deep core fueling, wall conditioning, materials effect on core (particularlyimportant in emerging concepts and steady-state devices)

¥ Control heat and particle flux transients, e.g. ELMs (all)


Steady State Issues in the MFE Roadmap

Steady-State

Integration

Burning Plasma


PlasmaScience &

Technology

Tokamak

ST

Stellarator RFP

FRC

Spheromak


Achieving Steady State MFE Plasmas

Two Key Issues (currently limiting progress toward SteadyState MFE):

¥ Plasma Controlto achieve and sustain a high-performance plasmaconfiguration.

¥ Power and Particle Handlingcompatible with a high-performance plasmaconfiguration.

¥ These issues are serious-- complementary approachesare needed for a successful resolution


Key Plasma Control Opportunities

Current profile control to prevent profile evolution to unstable configuration.

¥ Near term- complementary approaches:Ð NBI+ EC+bootstrap in AT ( DIII-D, next 3 years).Ð ICRF+LH+bootstrap in AT (C-Mod, 2002-08)

¥ Longer term: NSTX (2001+), KSTAR (2004+), etc.

Helical fields and 3D shaping for disruption suppression.

¥ Stellarator PoP program (proposed ). Complementary approaches:Ð High-bootstrap AT-like approach: NCSX QA, high β PoP experiment.Ð Low- bootstrap approach (CE-level test): QOS experiment.

MHD mode control for steady-state, high-beta scenarios.

¥ Control NTM with EC, RWM with feedback coils in AT. (DIIIÐD, next 3 yrs)

¥ Test No-wall ⇒ Wall performance gains in ST (NSTX)

¥ Stabilize kinks with resistive shell in RFP. (CE devices)


Key Plasma Control Opportunities, contÕd.

Current drive for startup and sustainment

¥ CHI+HHFW+NBI+bootstrap in ST (NSTX next 3-4 years).

¥ CHI in Spheromak (SSPX, next 3 years)

¥ OFCD in RFP (theory opportunity now; test in MST, next ~5 years)

¥ Rotating fields in FRC (U.ÊWash).

Local turbulence and transport control ⇒⇒⇒⇒ control pressure, bootstrap profiles; stability margins

¥ RF-driven flow shear most likely tool, e.g. MC-IBW in C-Mod (now).

More ideas exist; scientific and technological innovations are

urgently needed


Burning Plasma in the MFE Roadmap

Steady-State

Integration

Burning Plasma


PlasmaScience &

Technology

Tokamak

ST

Stellarator RFP

FRC

Spheromak


Why a Burning Plasma?

¥ The excitement of a magnetically-confined burning plasmaexperiment stems from the prospect of investigating andintegrating frontier physics in the areas of energetic particles,transport, stability, and plasma control, in a relevant fusionenergy regime. This is fundamental to the development offusion energy.

¥ Scientific understanding from a burning plasma experimentwill benefit related confinement concepts, and technologiesdeveloped for and tested in such a facility will benefit nearlyall approaches to magnetic fusion energy.


Frontier Physics to Investigate and Integrate in a Self-Heated Plasma

¥ Energetic ParticlesÐ Collective alpha-driven instabilities and associated alpha transport.

¥ TransportÐ Transport physics at dimensionless parameters relevant to a reactor

regime (L/ri)* : scaling of microtubulence, effects on transport

barriersÉ

¥ StabilityÐ Non-ideal MHD effects at high L/ri: resistive tearing modes, resistive

wall modes, particle kinetic effectsÉ

¥ Plasma ControlÐ Wide range of time-scales: feedback control, burn dynamics, current

profile evolution

¥ Boundary PhysicsÐ Power and particle handling, coupling to core

*L/ri is the system size divided by the Larmor radius.


Scientific Transferability

A well-diagnosed, flexible burning plasma experiment will address a broadrange of scientific issues and enable development and validation oftheoretical understanding applicable in varying degrees to other magneticconcepts

¥ Energetic particle density gradient driven instabilities

¥ Transport and burn control techniques

¥ Boundary Physics, power and particle handling issues


Burning Plasma Opportuni t ie s

¥ The tokamak is technically ready for a high gain burningplasma experiment

¥ The US has exciting opportunities to explore BP physics by:Ð Pursuing burning plasma physics through collaboration

on potential international facilities (JET Upgrade,IGNITOR and ITER-RC)

Ð By seeking a partnership position, if the ITERconstruction proceeds

Ð Continued design/studies of moderate cost burningplasma experiments (e.g., FIRE) capable of exploringadvanced regimes

Ð Exploiting the capability of existing and upgradedtokamaks to explore and develop advanced operatingregimes suitable for burning plasma experiments.


Magnetic concepts in the MFE Roadmap

Steady-State

Integration

Burning Plasma


PlasmaScience &

Technology

Tokamak

ST

Stellarator RFP

FRC

Spheromak


The Magnetic Concept Portfolio

High BT, q>1 Concepts (development status)Ð Conventional tokamak (PE)Ð Advanced tokamak (PE)Ð Electric Tokamak (CE)Ð Stellarator (PE)Ð Compact stellarator (PoP proposed)Ð Spherical Torus (PoP)

Challenge: Optimize stable, steady-state, high-performanceplasma using 2D and 3D shaping, MHD stability control, andprofile control.

Low BT, q<1 ConceptsÐ Reversed Field Pinch (CE; PoP proposed)Ð Spheromak (CE)Ð Field-Reversed Configuration (CE)

Challenge: Demonstrate adequate confinement for fusion energyand explore techniques to improve confinement and extendpulse duration.

CE

PoP

FED

PE

Concept Exploration

Proof of Principle

Performance Extension

Fusion Energy Development


Conventional Pulsed Tokamak (presently at PE)

¥ Prospective Fusion Energy BenefitsÐ Provides testbed for developing technology and generic fusion energy

scienceÐ Demonstrated stability and confinementÐ Mature experimental database, performance nearest goal of fusion

energy

¥ IssuesÐ Must avoid and mitigate disruptions and ELMS at operating β to

reduce forces and heat loadÐ Large size and costÐ Pulsed operation: cyclic heat and stress loads, requires energy

storage

CE

PoP

FED

PE


Advanced Tokamak (AT) (presently at PE)

¥ Prospective Fusion Energy Benefits− Steady state via high bootstrap current fraction

⇒ reduced cyclic stress− High performance at lower IP

⇒ reduced capital costs, reduced disruption loads− Builds on extensive tokamak database & understanding

• Issues− Need to develop profile control & feedback stabilization to sustain

equilibrium, stabilize MHD modes− Must avoid/mitigate disruptions and ELMs at high β− Compatibility with edge particle and power handling strategies

CE

PoP

FED

PE


Spherical Torus (ST) (presently at PoP)

¥ Prospective Fusion Energy BenefitsÐ Reduced B, high β ⇒ reduced capital costs, simpler maintenanceÐ Steady state via high bootstrap current fractionÐ Predicted intrinsic turbulence stabilizationÐ May provide near-term neutron source

¥ IssuesÐ Need to develop non-inductive current ramp-up & sustainmentÐ Center column resistive losses & radiation effectsÐ Need to develop profile control & feedback stabilization to sustain

equilibrium, stabilize wall modesÐ High divertor heat loadsÐ Must avoid/mitigate disruptions

CE

PoP

FED

PE


Compact Stellarator (CS) (proposed for PoP)

¥ Prospective Fusion Energy BenefitsÐ MHD stability, improved disruption stability and very low disruption

loads, very low recirculating power by 3D magnetic field shaping

Ð Reduced development costs by combining stellarator & tokamakcharacteristics & advantages at aspect ratio ~ 3 - 4

¥ IssuesÐ Demonstrate β-limit, low disruption loads & adequate confinement at

low aspect ratioÐ Compatibility with power and particle handling schemeÐ Non-planar, more costly coils. Adequate coil-plasma spacing for

reactors

CE

PoP

FED

PE


Reversed Field Pinch (RFP) (proposed for PoP)

¥ Prospective Fusion Energy Benefits− Reduced capital costs due to low B on coils, high engineering β− Do not need superconducting coils

¥ IssuesÐ Must reduce magnetic turbulenceÐ Must develop method to efficiently sustain all the current (no

significant bootstrap current)Ð Need to stabilize kink/resistive wall modes− Must develop reactor relevant power & particle handling

CE

PoP

FED

PE


Spheromak (presently at CE)

¥ Prospective Fusion Energy Benefits− Very simple compact geometry

⇒ reduced development capital costs− Possible sustainment by helicity injection

• Issues− Helicity injection may produce excessive magnetic turbulence

⇒ plasma transport− Need to stabilize kink/resistive wall modes− Need to develop adequate power and particle handling, impurity

control

CE

PoP

FED

PE


MFE Provides a Path to an Optimized Energy Source

¥ The portfolio of magnetic configurations provides an opportunity topursue a broad range of important scientific issues for Fusion Energy

¥ The development of physics understanding with predictive capabilityleads to rapid progress in the science base for Fusion energy and rapidprogress in the individual magnetic configurations

¥ A burning plasma experiment offers the prospect of investigating andintegrating frontier physics in the areas of energetic particles, transport,stability, and plasma control in a relevant fusion energy regime.

¥ Scientific understanding and innovation are key features of themagnetic fusion energy program. Together these are leading toattractive configurations for the production of fusion energy.

july 11 -- july 23, 1999 snowmass village, colorado in magnetic confinement … · 1999. 8. 2. ·...

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